Silvery white interference pigments having a high luster and based on transparent substrate laminae

ABSTRACT

The present invention relates to interference pigments based on coated flake-form substrates which are distinguished by the fact in that they comprise 
         (A) a layer of SiO 2  having a layer thickness of 5-350 nm, (B) a high-refractive-index coating having a refractive index n of &gt;1.8 and/or (C) an interference system consisting of alternating high- and low-refractive-index layers and optionally (D) an outer protective layer, and to the use thereof in paints, coatings, automotive paints, powder coatings, printing inks, security printing inks, plastics, ceramic materials, glasses, paper, in toners for electrophotographic printing processes, in seed, in greenhouse sheeting and tent awnings, as absorbers in the laser marking of paper and plastics, in cosmetic formulations, for the preparation of pigment pastes with water, organic and/or aqueous solvents, and for the preparation of pigment preparations and dry preparations.

The present invention relates to interference pigments based onmulti-coated flake-form substrates and to the use thereof, inter alia inpaints, coatings, printing inks, plastics and in cosmetic formulations.

Interference pigments are employed as lustre or effect pigments in manyareas of industry, in particular in decorative coating, in plastics, inpaints, coatings, printing inks and in cosmetic formulations. Pigmentswhich exhibit an angle-dependent colour play between a plurality ofinterference colours are, owing to their colour play, of particularinterest for automotive paints, counterfeiting-proof securities and indecorative cosmetics.

Interference pigments generally consist of flake-form supports which arecoated with thin metal-oxide layers. The optical effect of thesepigments is based on directed reflection of light at the flakes whichare predominantly aligned parallel. Reflection of the light at theinterfaces of layers of different refractive index causes the formationof interference colours (G. Pfaff in High Performance Pigments,Wiley-VCH Verlag, Weinheim, 2002, Chap. 7, Special Effect Pigments).

U.S. Pat. No. 3,331,699 describes pearlescent pigments having brightinterference colours and an intense glitter effect. The pigments arebased on glass flakes which are coated with a translucent,high-refractive-index metal-oxide layer. Suitable metal oxides are ZrO₂,TiO₂ and Cr₂O₃. The colour of the pigments here is dependent on themetal oxide selected and on the thickness of the metal-oxide layer. Manyinterference colours from silver via gold, violet, blue and green can beproduced by different layer thicknesses. The glass composition here isnot crucial for the coating with a metal oxide. In order that a coatingcan be achieved at all, however, the presence of a nucleating agent,such as, for example, tin dioxide or boehmite, on the glass surface isabsolutely necessary.

WO 97/46624 describes pearlescent pigments which are based on glassflakes and are coated with TiO₂ or Fe₂O₃.

Lustrous pigments are only obtained if the thin metal layer on thesupport is very smooth and uniform. WO 97/46624 states that the coatingmust adhere strongly to the support in order that there is no fractureand/or detachment of the coating during processing. The user perceivesinadequate adhesion of the metal-oxide layer to the support as poormechanical stability of the pigment since the gloss drops considerablyduring mechanical stressing, for example due to shear forces duringrubbing of the pigment in a cosmetic preparation on the skin, in theprinting process, in the production of pigment granules or duringpumping round the ring line of a paint shop. Even a small proportion ofdamaged pigment particles causes significant impairment of thecoloristic properties of the pigment application.

Pigments from U.S. Pat. No. 3,331,699 and WO 97/46624 can, owing to theglass types used, only be calcined at temperatures below 600° C.However, the temperature of 600° C. here does not represent a sharplimit, but instead is a compromise of technical requirements which aredifficult to combine.

Pigments with TiO₂ layers which have been calcined at low temperatureexhibit increased photoactivity, in particular on incorporation intoplastic systems, and are not suitable for articles subjected to intenseor long-lasting exposure to light. The causes of this are the porosityand the large active surface areas of the precipitated metal-oxidelayers, which only consolidate at calcination temperatures from 700° C.This consolidation results in reduced porosity of the metal-oxide layersand at the same time in an increase in the refractive indices and thusin improved optical properties of the pigments. At higher temperatures,however, the pigments are destroyed by the considerable softening of theglass cores and associated deformation of the flakes as well as fractureand/or detachment of the coating. Even at calcination temperatures of600° C. or below, a reduction in the layer adhesion to the support canoccur, impairing the mechanical stability of the pigments. Such pigmentscan only be employed to a limited extent in practice.

EP 0 753 545 B1 discloses goniochromatic lustre pigments based onhigh-refractive-index, transparent, non-metallic, flake-form substrateswhich comprise at least one layer package comprising a colourlesscoating having a refractive index n of ≦1.8 and a reflective,selectively or non-selectively absorbent coating. Suitable substrates,such as, for example, flake-form iron oxide, BiOCl, TiO₂— or ZrO₂-coatedmica, have a refractive index n of ≧2. The goniochromatic lustrepigments exhibit an angle-dependent colour play between a plurality ofintense interference colours and thus a pronounced colour flop, which isadvantageous in many industrial applications, is frequently desired indecorative applications, but is undesired in the great majority ofapplications of pearlescent pigments.

WO 01/30920 discloses gold- and orange-coloured interference pigments ofhigh hiding power which are distinguished by the fact that flake-formsubstrates are coated with at least two layer sequences comprising alow-refractive-index layer and a high-refractive-index layer comprisinga metal-oxide mixture of Fe₂O₃ and TiO₂. The materials mentioned for thelow-refractive-index coating are SiO₂, Al₂O₃, AlO(OH), B₂O₃, MgF₂,MgSiO₃ or mixtures of these oxides. However, the essential features inthe case of the pigments from WO 01/30920 are the body colour and thehiding power due to the high inherent absorption of the mixed-oxidelayers. Thus, only gold- and orange-coloured pigments of high hidingpower are accessible. Silver-white pigments having high gloss are justas inaccessible as high-gloss pigments having bright interferencecolours and high transparency. There is a great demand in printingtechnology, in plastics, for surface coatings and in cosmetics for, inparticular, silver-white pigments having improved gloss.

The object of the present invention is to provide silver-whiteinterference pigments having high gloss and high-gloss interferencepigments having bright interference colours which are mechanicallystable and simple to prepare and are distinguished by furtheradvantageous technical properties.

Surprisingly, it has now been found that interference pigments based ontransparent flake-form substrates have improved gloss and exhibit moreintense colours if the flakes are coated with a first layer of SiO₂, towhich a high-refractive-index layer, such as, for example, titaniumdioxide, titanium suboxide, zirconium oxide, tin oxide, chromium oxide,Fe₂O₃ or Fe₃O₄, is then applied.

In addition to their higher gloss, pigments according to the inventionhaving glass flakes as support are distinguished over the coated glassflakes from the prior art by significantly improved calcinationbehaviour. The interference pigments according to the invention based onglass flakes can be calcined at temperatures >700° C. withoutdeformation or destruction of the flake structure occurring.

The interference pigments according to the invention are thus clearlysuperior to the pigments from the prior art not only with respect totheir optical properties, such as gloss and tinting strength, but alsoin their technical properties, such as, for example, mechanicalstability and photostability.

The invention therefore relates to interference pigments based onflake-form substrates which are distinguished by the fact that theycomprise

-   -   (A) a layer of SiO₂ having a layer thickness of 5-350 nm,    -   (B) a high-refractive-index coating having a refractive index n        of >1.8        and/or    -   (C) an interference system consisting of alternating high- and        low-refractive-index layers        and optionally    -   (D) an outer protective layer.

The invention furthermore relates to the use of the interferencepigments according to the invention in paints, coatings, in particularautomotive paints, powder coatings, printing inks, security printinginks, plastics, ceramic materials, glasses, paper, in toners forelectrophotographic printing processes, in seed, in greenhouse sheetingand tent awnings, as absorbers in the laser marking of paper andplastics, and in cosmetic formulations. Furthermore, the pigmentsaccording to the invention are also suitable for the preparation ofpigment pastes with water, organic and/or aqueous solvents, pigmentpreparations and for the preparation of dry preparations, such as, forexample, granules, chips, pellets, briquettes, etc. The dry preparationsare particularly suitable for printing inks and in cosmetics.

Suitable base substrates for the interference pigments according to theinvention are colourless or selectively or non-selectively absorbentflake-form substrates. Suitable substrates are, in particular,phyllosilicates, such as natural and/or synthetic mica, talc, kaolin,flake-form iron or aluminium oxides, glass flakes, SiO₂ flakes, TiO₂flakes, graphite flakes, synthetic support-free flakes, titaniumnitride, titanium silicide, liquid crystal polymers (LCPs), holographicpigments, BiOCl and flake-form mixed oxides, or mixtures thereof.Particularly preferred substrates are glass flakes, mica flakes andAl₂O₃ flakes.

Particular preference is given to glass flakes owing to theirparticularly smooth surface and their very high reflectivity.

The size of the base substrates is not crucial per se and can be matchedto the particular application. In general, the flake-form substrateshave a thickness of between 0.005 and 10 μm, in particular between 0.1and 5 μm. The dimension in the two other ranges is usually 1-500 μm,preferably 2-300 μm and in particular 20-200 μm. Preferred smallerparticle sizes are furthermore those in the range 1-100 μm, inparticular 5-60 μm and 1-15 μm.

Particular preference is given to glass flakes having an averagethickness of <2 μm. Thicker flakes generally cannot be employed incustomary printing processes and in demanding finishes. The glass flakespreferably have thicknesses of <1 μm, in particular <0.9 μm, veryparticularly preferably <0.7 μm. Particular preference is given to glassflakes having thicknesses of 0.25-0.7 μm. The diameter of the glassflakes is preferably 5-300 μm, particularly preferably 10-100 μm,furthermore 5-60 μm. Glass flakes having these dimensions can beprepared, for example, by the process described in EP 0 289 240.

The glass flakes can consist of all glass types known to the personskilled in the art, such as, for example, window glass, C glass, Eglass, ECR glass, Duran® glass, laboratory equipment glass or opticalglass. Particular preference is given to E glass or ECR glass. Therefractive index of the glass flakes is preferably 1.45-1.80, inparticular 1.50-1.70.

However, the chemical composition of the glass flakes is, owing to thecoating with an SiO₂ layer (layer (A)), of secondary importance for thefurther coatings and the resultant technical properties of the pigments.The SiO₂ coating protects the glass surface against chemicalmodification, such as swelling, leaching-out of glass constituents ordissolution in the aggressive acidic coating solutions.

During the calcination process, an intimate bond between the chemicallyrelated materials arises in the case of the glass flakes at theinterface between glass body and precipitated-on SiO₂. Owing to the highsoftening temperature, the precipitated-on SiO₂ sheath gives thesubstrates the requisite mechanical stability, even in the case ofcalcination above 700° C. The adhesion of the high-refractive-indexcoating(s) following the SiO₂ layers is also very good, even above 700°C.

The thickness of layer (A) on the substrate can be varied in broadranges depending on the desired effect. Layer (A) has thicknesses of5-350 nm, preferably 5-150 nm. For control of gloss and tintingstrength, layer thicknesses of 30-100 nm are preferred.

The SiO₂ layer may also be doped with carbon black particles, inorganiccoloured pigments and/or metal particles if this doping is stable in airor under an inert gas at temperatures >700° C. The proportion of dopantin the SiO₂ matrix is then 1-30% by weight, preferably 2-20% by weight,in particular 5-20% by weight.

The high-refractive-index coating (B) preferably consists of metaloxides and/or suboxides.

Layer (B) preferably consists of metal oxides, such as, for example,TiO₂, ZrO₂, SnO₂, ZnO, Ce₂O₃, Fe₂O₃, Fe₃O₄, Cr₂O₃, CoO, Co₃O₄, VO₂,V₂O₃, NiO, furthermore of titanium suboxides (TiO₂ partially reducedwith oxidation states of from <4 to 2, such as the lower oxides Ti₃O₅,Ti₂O₃ to TiO), titanium oxynitrides, FeO(OH), thin semitransparent metallayers, for example comprising Al, Fe, Cr, Ag, Au, Pt or Pd, orcombinations thereof. The TiO₂ layer may be in the rutile or anatasemodification, preference being given to rutile layers. Rutile ispreferably prepared by the process from EP 0 271 767.

Layer (B) is preferably a metal-oxide layer, in particular TiO₂, Fe₂O₃,Fe₃O₄, SnO₂, ZrO₂ or Cr₂O₃. Particular preference is given to titaniumdioxide.

Layer (B) can of course also consist of a plurality ofhigh-refractive-index layers. Layer (B) preferably consists of only onelayer, furthermore of two layers.

The thickness of the high-refractive-index layers depends on the desiredinterference colour. The thickness of layer (B) is preferably 60-300 nm.Combination of the thin SiO₂ layer with a high-refractive-indexmetal-oxide layer enables, for example, interference colours from puresilver-white via gold to intense green to be obtained.

Further high- and/or low-refractive-index layers (layer C) can beapplied alternately to layer (B). The number of layers is preferablytwo, furthermore three, four, five, six or seven layers.

In particular, interference packages consisting of high- andlow-refractive-index layers on layer (B) result in pigments havingincreased gloss and a further increased interference colour.

Instead of layer (B), an interference system comprising alternatinghigh- and low-refractive-index layers (layer C) can also be applieddirectly to the SiO₂ layer.

The thickness of the individual layers of high or low refractive indexis in turn essential for the optical properties of the pigment. For theinterference pigment according to the invention, the thicknesses of theindividual layers must be set precisely with respect to one another. Thethickness of layer (C) is 40-800 nm, preferably 60-600 nm, in particular100-400 nm.

Suitable materials as high-refractive-index layer are all thosementioned for layer (B).

Suitable colourless low-refractive-index materials for coating (C) arepreferably metal oxides or the corresponding oxide hydrates, such as,for example, SiO₂, Al₂O₃, AlO(OH), B₂O₃, compounds such as MgF₂, MgSi₃,or a mixture of the said metal oxides. The interference system of layer(C) is, in particular, a TiO₂—SiO₂—TiO₂ layer sequence.

Furthermore, the interference pigments according to the invention mayalso have a semitransparent metal layer as outer layer. Coatings of thistype are known, for example, from DE 38 25 702 A1. The metal layers arepreferably chromium or aluminium layers having layer thicknesses of 5-25nm.

The high-refractive-index layers (B) and/or (C) used can of course alsobe colourless high-refractive-index materials, such as, for example,metal oxides, in particular TiO₂ and ZrO₂, which have been coloured withtemperature-stable absorbent colorants, such as, for example, red ironoxide or Thenard's Blue. The absorbent colorants may also be applied tothe high-refractive-index coating in the form of a film. Berlin Blue andCarmine Red are preferably applied to the pre-calcined TiO₂ and ZrO₂layers. Examples of coatings of this type are disclosed, for example, inDE 23 13 332.

Particularly preferred interference pigments are mentioned below:

glass flakes+SiO₂+TiO₂

glass flakes+SiO₂+Fe₂O₃

glass flakes+SiO₂+Fe₃O₄

glass flakes+SiO₂+Cr₂O₃

glass flakes+SiO₂+TiO₂+Berlin Blue

glass flakes+SiO₂+TiO₂+Carmine Red

glass flakes+SiO₂+TiO₂+SiO₂+TiO₂

glass flakes+SiO₂+TiO₂+Cr

mica flakes+SiO₂+TiO₂

mica flakes+SiO₂+Fe₂O₃

mica flakes+SiO₂+Fe₃O₄

mica flakes+SiO₂+Cr₂O₃

mica flakes+SiO₂+TiO₂+Berlin Blue

mica flakes+SiO₂+TiO₂+Carmine Red

mica flakes+SiO₂+TiO₂+SiO₂+TiO₂

mica flakes+SiO₂+TiO₂+Cr

Al₂O₃ flakes+SiO₂+TiO₂

Al₂O₃ flakes+SiO₂+Fe₂O₃

Al₂O₃ flakes+SiO₂+Fe₃O₄

Al₂O₃ flakes+SiO₂+Cr₂O₃

Al₂O₃ flakes+SiO₂+TiO₂+Berlin Blue

Al₂O₃ flakes+SiO₂+TiO₂+Carmine Red

Al₂O₃ flakes+SiO₂+SnO₂+TiO₂+Carmine Red

Al₂O₃ flakes+SiO₂+TiO₂+SiO₂+TiO₂

Al₂O₃ flakes+SiO₂+TiO₂+Cr

Of the particularly preferred interference pigments, the coated glassflakes are particularly preferred, furthermore the coated Al₂O₃ flakes.

The term high-refractive-index coatings is taken to mean layers having arefractive index of >1.8, and the term low-refractive-index layers istaken to mean those having n≦1.8.

The interference pigments according to the invention can generally beprepared relatively easily.

The metal-oxide layers are preferably applied by wet-chemical methods,it being possible to use the wet-chemical coating methods developed forthe preparation of pearlescent pigments. Methods of this type aredescribed, for example, in DE 14 67 468, DE 19 59 988, DE 20 09 566, DE22 14 545, DE 22 15 191, DE 22 44 298, DE 23 13 331, DE 15 22 572, DE 3137 808, DE 31 37 809, DE 31 51 343, DE 31 51 354, DE 31 51 355, DE 32 11602, DE 32 35 017 or in further patent documents and other publicationsknown to the person skilled in the art.

In the case of wet coating, the substrate particles are suspended inwater, and one or more hydrolysable metal salts or a water-glasssolution are added at a pH which is suitable for hydrolysis, this pHbeing selected in such a way that the metal oxides or metal oxidehydrates are precipitated directly onto the flakes without secondaryprecipitations occurring. The pH is usually kept constant bysimultaneous metering-in of a base and/or acid. The pigments aresubsequently separated off, washed and dried at 50-150° C. for 6-18hours and optionally calcined for 0.5-3 hours, it being possible for thecalcination temperature to be optimised with respect to the coatingpresent in each case. In general, the calcination temperatures arebetween 700 and 1000° C., preferably between 700 and 900° C. If desired,the pigments can be separated off, dried and optionally calcined afterapplication of individual coatings and then re-suspended again forprecipitation of the further layers.

The precipitation of the SiO₂ layer onto the substrate is generallycarried out by addition of a potassium or sodium water-glass solution ata suitable pH.

Furthermore, the coating can also be carried out in a fluidised-bedreactor by gas-phase coating, it being possible correspondingly to usethe processes proposed, for example, in EP 0 045 851 and EP 0 106 235for the preparation of pearlescent pigments.

The hue of the interference pigments can be varied in very broad limitsthrough the different choice of the coating amounts or the layerthicknesses resulting therefrom. Fine tuning for a certain hue can beachieved beyond the pure choice of amount by approaching the desiredcolour under visual or measurement technology control.

In order to increase the light, water and weather stability, it isfrequently advisable, depending on the area of application, to subjectthe finished pigment to post-coating or post-treatment. Suitablepost-coatings or post-treatments are, for example, the processesdescribed in German Patent 22 15 191, DE-A 31 51 354, DE-A 32 35 017 orDE-A 33 34 598. This post-coating (layer D) further increases thechemical and photochemical stability or simplifies the handling of thepigment, in particular the incorporation into various media. In order toimprove the wettability, dispersibility and/or compatibility with theuser media, it is possible, for example, for functional coatings ofAl₂O₃ or ZrO₂ or mixtures thereof to be applied to the pigment surface.Furthermore, organic post-coatings are possible, for example withsilanes, as described, for example, in EP 0090259, EP 0 634 459, WO99/57204, WO 96/32446, WO 99/57204, U.S. Pat. No. 5,759,255, U.S. Pat.No. 5,571,851, WO 01/92425 or in J. J. Ponjeé, Philips Technical Review,Vol. 44, No. 3, 81 ff. and P. H. Harding J. C. Berg, J. Adhesion Sci.Technol. Vol. 11 No. 4, pp. 471-493.

Compared with the pigments from the prior art without an SiO₂ layer onthe substrate, the pigments according to the invention are distinguishedby their higher chroma (tinting strength C*), their higher gloss (Lvalue) and pronounced glitter effects, in particular in the case of thepigments based on glass or Al₂O₃ flakes. Compared with thegoniochromatic pigments from EP 0 753 545 B1, the interference pigmentsaccording to the invention exhibit no or only low angle dependence ofthe colour.

Compared with the teaching from WO 01/30920, crucial advantages withrespect to gloss and mechanical stability of the pigments according tothe invention only arise for SiO₂ as material for the first coating ofthe support. Beyond the disclosure content of WO 01/30920, silver-whitepigments and high-gloss interference pigments having bright interferencecolours, such as red, blue or green, are accessible with the invention.The pigments according to the invention can advantageously be blendedwith absorption pigments or colours owing to their transparency.Combinations of this type enable unusual colour impressions to beachieved in a particularly simple manner.

The pigments according to the invention are compatible with amultiplicity of colour systems, preferably from the area of paints,coatings and printing inks and cosmetic formulations. For thepreparation of printing inks for, for example, gravure printing,flexographic printing, offset printing and offset overvarnishing, amultiplicity of binders, in particular water-soluble grades, as sold,for example, by BASF, Marabu, Pröll, Sericol, Hartmann, Gebr. Schmidt,Sicpa, Aarberg, Siegberg, GSB-Wahl, Follmann, Ruco or Coates Screen INKSGmbH, is suitable. The printing inks can be water-based orsolvent-based. The pigments are furthermore also suitable for the lasermarking of paper and plastics and for applications in the agriculturalsector, for example for greenhouse sheeting, and, for example, for thecolouring of tent awnings.

Since the interference pigments according to the invention combine highgloss with intense interference colours and highly pronounced glittereffects, particularly effective effects can be achieved with them invarious application media, for example in cosmetic formulations, suchas, for example, nail varnishes, lipsticks, compact powders, gels,lotions, soaps, toothpastes, in paints, such as, for example, automotivepaints, industrial coatings and powder coatings, and in plastics and inceramics.

Owing to the good skin feeling and the very good skin adhesion, thepigments according to the invention are suitable both for personal careapplications, such as, for example, body lotions, emulsions, shampoos,soaps, etc., and, in particular, for decorative cosmetics.

It goes without saying that, for the various applications, themultilayered pigments according to the invention can also advantageouslybe used in blends with organic dyes, organic pigments or other pigments,such as, for example, transparent and opaque white, coloured and blackpigments, and with flake-form iron oxides, organic pigments, holographicpigments, LCPs (liquid crystal polymers) and conventional transparent,coloured and black lustre pigments based on metal oxide-coated mica andSiO₂ flakes, etc. The pigments according to the invention can be mixedin any ratio with commercially available pigments and fillers.

Fillers which may be mentioned are, for example, natural and syntheticmica, nylon powder, pure or filled melamine resins, talc, SiO₂, glasses,kaolin, oxides or hydroxides of aluminium, magnesium, calcium or zinc,BiOCl, barium sulfate, calcium sulfate, calcium carbonate, magnesiumcarbonate, carbon, and physical or chemical combinations of thesesubstances.

There are no restrictions regarding the particle shape of the filler. Itcan be, for example, flake-form, spherical or needle-shaped inaccordance with requirements.

It is of course also possible for the pigments according to theinvention to be combined in the formulations with cosmetic raw materialsand assistants of any type. These include, inter alia, oils, fats, filmformers, preservatives and assistants which generally determine thetechnical properties, such as, for example, thickeners and rheologicaladditives, such as, for example, bentonites, hectorites, silicondioxides, Ca silicates, gelatines, high-molecular-weight carbohydratesand/or surface-active assistants, etc.

The formulations comprising the pigments according to the invention canbelong to the lipophilic, hydrophilic or hydrophobic type. Inheterogeneous formulations having discrete aqueous and non-aqueousphases, the pigments according to the invention may be present in ineach case only one of the two phases or alternatively distributed overboth phases.

The pH values of the formulations can be between 1 and 14, preferablybetween 2 and 11 and particularly preferably between 5 and 8.

No limits are set for the concentrations of the pigments according tothe invention in the formulation. They can be—depending on theapplication—between 0.001 (rinse-off products, for example shower gels)and 100% (for example gloss-effect articles for particularapplications).

The pigments according to the invention may furthermore also be combinedwith cosmetic active ingredients. Suitable active ingredients are, forexample, insect repellents, UV A/BC protective filters (for example OMC,B3 or MBC), anti-ageing active ingredients, vitamins and derivativesthereof (for example vitamin A, C, E etc.), self-tanning agents (forexample DHA, erythrulose, inter alia) and further cosmetic activeingredients, such as, for example, bisabolol, LPO, ectoin, emblica,allantoin, bio-flavonoids and derivatives thereof.

The pigments according to the invention are furthermore suitable for thepreparation of flowable pigment preparations and dry preparations, inparticular for printing inks and cosmetic applications, comprising oneor more pigments according to the invention, binders and optionally oneor more additives.

The invention thus also relates to the use of the pigments informulations such as paints, coatings, automotive paints, powdercoatings, printing inks, security printing inks, plastics, ceramicmaterials, glasses, paper, in toners for electrophotographic printingprocesses, in seed, in greenhouse sheeting and tent awnings, asabsorbers in the laser marking of paper and plastics, in cosmeticformulations, for the preparation of pigment pastes with water, organicand/or aqueous solvents, and for the preparation of pigment preparationsand dry preparations, such as, for example, granules.

The following examples are intended to explain the invention in greaterdetail, but without restricting it.

EXAMPLES Example 1

150 g of glass flakes (glass A from Table 1) having an average layerthickness of 700 nm are heated to 75° C. with stirring in 1.9 l ofdeionised water. The pH of the suspension is then adjusted to 7.5 using5% hydrochloric acid. Sodium water-glass solution (112 g of sodiumwater-glass solution comprising 26.8% of SiO₂ dissolved in 112 g ofdeionised water) is subsequently added dropwise, during which the pH iskept constant at 7.5 by simultaneous metered addition of 5% hydrochloricacid. When the addition is complete, the mixture is stirred for afurther 0.5 hour. The pH of the suspension is then adjusted to 1.8, thesuspension is stirred for a further 15 minutes, and tin tetrachloridesolution in hydrochloric acid (3 g of SnCl₄*5H₂O, dissolved in 15 ml of25% hydrochloric acid and 85 ml of deionised water) is added dropwise,during which the pH is kept constant by simultaneous dropwise additionof 32% sodium hydroxide solution. When the addition is complete, themixture is stirred for a further 15 minutes.

This is followed by metered addition of 30% titanium tetrachloridesolution, during which the pH is kept constant by simultaneous dropwiseaddition of 32% sodium hydroxide solution. The coloristic propertiesduring preparation of the pigment are monitored by colour measurementduring the process, and the precipitation process is controlled inaccordance with the hue (hue angle arc tan b*/a*). When the desiredsilver end point has been reached, the mixture is stirred for a further15 minutes. The pigment comprises 20% of precipitated SiO₂, based on theglass flakes.

The product is filtered off, washed, dried at 150° C. and calcinedat >700° C.

The finished pigment is incorporated into a commercially availablenitro-cellulose lacquer, and paint cards are prepared. The paint cardsexhibit a very pure silver-white with high gloss. TABLE 1 Glasscompositions in % Constituent Glass A Glass B SiO₂ 64 60 Al₂O₃ 5 5 CaO6.2 7.7 MgO 2.2 5.2 B₂O₃ 5.3 6.1 Na₂O + K₂O 13.5 16 ZnO 3.7 0 FeO/Fe₂O₃0.1 0

EXAMPLE 2

A silver-white pigment is prepared by the process described inExample 1. Instead of glass flakes of composition A from Table 1, glassflakes of composition B having the same thickness and size distribution(20-200 μm) are used. The titanium dioxide coating is carried out to thesame end point as in Example 1. The pigments obtained cannot bedistinguished visually from those from Example 1.

Examples 3-5

Silver-white pigments having the following proportions by weight ofSiO₂, based on the glass flakes, are prepared by the procedure indicatedin Example 1:

Example 3: 2% of SiO₂ by metered addition of 11.5 g of water-glasssolution dissolved in 11.5 g of water

Example 4: 5% of SiO₂ by metered addition of 28 g of water-glasssolution dissolved in 28 g of water

Example 5: 10% of SiO₂ by metered addition of 56 g of water-glasssolution dissolved in 56 g of water

The titanium dioxide coatings are carried out to the same hue as inExperiments 1 and 2.

Examples 6 and 7 Comparative Examples without a First SiO₂ Layer

150 g of glass flakes of composition A from Table 1 having an averagelayer thickness of 700 nm are heated to 75° C. with stirring in 1.9 1 ofdeionised water. The pH of the suspension is adjusted to pH 1.8 usinghydrochloric acid. Tin tetrachloride solution in hydrochloric acid (4.5g of SnCl₄*5 H₂O dissolved in 22.5 ml of 25% hydrochloric acid and 128ml of deionised water) is subsequently added dropwise, during which thepH is kept constant by simultaneous dropwise addition of 32% sodiumhydroxide solution. When the addition is complete, the mixture isstirred for a further 15 minutes. This is followed by metered additionof 30% titanium tetrachloride solution, during which the pH is keptconstant by simultaneous dropwise addition of 32% sodium hydroxidesolution. When the desired silver end point has been reached, themixture is stirred for a further 15 minutes.

The product is filtered off, washed and dried at 150° C. A sample of thepigment is calcined at 600° C. (Example 6), and another is calcined at700° C. (Example 7), in each case for 60 minutes.

The finished pigments are incorporated into a commercially availablenitro-cellulose lacquer, and paint cards are prepared using the lacquer.With the pigment calcined at 600° C., the paint cards exhibit a puresilver-white with good gloss, while in the case of the pigment calcinedat 700° C., the gloss is significantly reduced.

Example 8 Comparative Example

150 g of glass flakes of composition A from Table 1 having an averagelayer thickness of 700 nm are heated to 75° C. with stirring in 1.9 l ofdeionised water. The pH is adjusted to 5.5. 180 ml of aluminium chloridesolution in hydrochloric acid (18 g of aluminium chloride hexahydrate)are added dropwise at 75° C. with stirring, during which the pH is heldat 5 using sodium hydroxide solution. When the addition is complete, themixture is stirred at 75° C. for a further 2 hours. The coated glassflakes are filtered off, washed, dried at 150° C. and dewatered at 400°C. for 30 minutes. After cooling, the glass flakes coated with aluminiumoxide (about 5% of Al₂O₃) are processed further using titanium by theprocedure indicated in Example 6 to give a silver-white pigment.

Compared with the pigment in accordance with the prior art from Example6, the pigment from Example 8 shows absolutely no improvement in gloss,and compared with the pigments having an SiO₂ layer, the pigmentexhibits significantly lower gloss. TABLE 2 Gloss values L and chroma C*of the silver-white pigments from Examples 1-8, measured on a blackbackground Experiment Gloss value L Chroma C* 1 76 3.5 2 76 3.6 3 732.16 4 75 2.82 5 76 3.4 6 (comparison) 66 1.9 7 (comparison) 56 1.67 8(comparison) 62 1.8

Example 9 Testing of the Mechanical Stability

The abrasion stability of the pigment in cosmetic preparations can betested in a practical test. It is determined here whether the mechanicalstability of a pigment is sufficient for use, for example, in compactpowders or creams. As a rapid test, rubbing of a pigment sample with thefinger on the palm of the hand has proven successful. In the case oflayer detachment or fracture of the pigment particles by the rubbing,the gloss of the rubbed sample is reduced or completely lost. Thedecrease in gloss is assessed visually in steps from 1 to 5, where step1 denotes no change or an increase in gloss during rubbing and step 5denotes strong matting. Step 3 is regarded as usable to a limited extentfor practice, 4 and 5 are regarded as unusable.

The pigments from Examples 1-7 are subjected to an abrasion test of thistype. The results are shown in Table 3 and show that only the pigmentsaccording to the invention having an SiO₂ layer have adequate mechanicalstability for cosmetic applications. TABLE 3 Abrasion stability AbrasionPigment Glass type SiO₂ layer stability Experiment 1 (invention) Aapprox. 70 nm 1 Experiment 2 (invention) B approx. 70 nm 1 Experiment 3(invention) A approx. 7 nm 3 Experiment 4 (invention) A approx. 17 nm 2Experiment 5 (invention) A approx. 35 nm 1 Experiment 6 (comparison) A 05 Experiment 7 (comparison) A 0 5

Example 10 Comparative Experiment

100 g of aluminium oxide flakes (prepared as described in EP 0 763 573B1, Example 2) are suspended in 2 litres of deionised water in a 5 litrelaboratory reactor. 200 ml of aqueous SnCl₄ solution (36 g of SnCl₄ perlitre of solution) are added dropwise at 3 ml/min at 75° C. withstirring. The pH of the suspension is held at 1.8 by metered addition ofsodium hydroxide solution. The mixture is stirred for a further 10minutes, and aqueous titanium tetrachloride solution (125 g ofTiCl₄/litre of solution) is then metered in at a rate of 3 ml/min,during which the pH is held at 1.7-1.9 by addition of sodium hydroxidesolution. In this way, the aluminium oxide flakes are coated with atitanium dioxide layer, where, with increasing layer thickness of thetitanium dioxide layer, firstly a silver-white and then colouredinterference colours of first to third order are formed. The coloristicproperties of the interference pigment are measured during the coatingprocess with the aid of a gap-form measurement cell which is connectedto the reactor and through which reaction mixture is pumped continuouslyduring the coating. During flow through the gap of the measurementchamber, the pigment flakes are aligned substantially parallel to theflow direction and are measured against a black background. Using acommercially available Minolta CR 300 colour measurement cell, the lightreflected at an angle after flash illumination is measured. Themeasurement data are converted into CIELAB values in accordance with DIN5033 Part 3 and displayed. In this way, the coloristic properties of thepigment can be determined at any stage of the coating. FIG. 1 shows thecourse of the coloristic properties of the coating in the form of ana*/b* diagram. In the system, +a values represent red, −a valuesrepresent green, +b values represent yellow and −b values representblue. The measurement curve begins at the coordinate origin and showsthe interference colour corresponding to the titanium dioxide coating.The chroma of the pigments is greater the further the colour location isseparated from the coordinate origin.

Example 11

100 g of aluminium oxide flakes (prepared as described in EP 0 763 573B1, Example 2) are suspended in 1.6 litres of deionised water in thelaboratory reactor from Example 10. The pH of the suspension is set to8, and sodium water-glass solution (190 g of sodium water-glass solutioncomprising 26.8% of SiO₂ dissolved in 190 g of deionised water) issubsequently added dropwise, during which the pH is kept constant at 8by simultaneous metered addition of 5% hydrochloric acid. When theaddition is complete, the mixture is stirred for a further 0.5 hour. ThepH of the suspension is then adjusted to 1.8 using 5% hydrochloric acid,the mixture is stirred for a further 15 minutes, and tin tetrachloridesolution in hydrochloric acid (4.5 g of SnCl₄*5 H₂O dissolved in 22.5 mlof 25% hydrochloric acid and 128 ml of deionised water) is addeddropwise, during which the pH is kept constant by simultaneous dropwiseaddition of 32% sodium hydroxide solution. When the addition iscomplete, the mixture is stirred for a further 15 minutes, and aqueoustitanium tetrachloride solution (125 g of TiC₄/litre of solution) isthen metered in at a rate of 3 ml/min, during which the pH is held at1.7-1.9 by addition of sodium hydroxide solution. The coloristicproperties of the pigment are measured as in Example 10 during the TiO₂coating. The comparison shows that the pigments according to theinvention have significantly better chroma (“tinting strength”) thanpigments from the prior art (FIG. 2). In addition, the pigmentsaccording to the invention exhibit significantly higher gloss.

Example 12

150 g of glass flakes (glass C from Table 4) having an average layerthickness of 900 nm are heated to 75° C. with stirring in 1.9 l ofdeionised water. The pH of the suspension is then adjusted to 7.5 using5% hydrochloric acid. Sodium water-glass solution (112 g of sodiumwater-glass solution comprising 26.8% of SiO₂ dissolved in 112 g ofdeionised water) is subsequently added dropwise, during which the pH iskept constant at 7.5 by simultaneous metered addition of 5% hydrochloricacid. When the addition is complete, the mixture is stirred for afurther 0.5 hour. The pH of the suspension is then adjusted to 1.8, themixture is stirred for a further 15 minutes, and tin tetrachloridesolution in hydrochloric acid (3 g of SnCl₄*5 H₂O dissolved in 15 ml of25% hydrochloric acid and 85 ml of deionised water) is added dropwise,during which the pH is kept constant by simultaneous dropwise additionof 32% sodium hydroxide solution. When the addition is complete, themixture is stirred for a further 15 minutes.

This is followed by metered addition of 30% titanium tetrachloridesolution, during which the pH is kept constant by simultaneous dropwiseaddition of 32% sodium hydroxide solution. The coloristic properties aremonitored during preparation of the pigment by colour measurement duringthe process, and the precipitation process is controlled in accordancewith the hue (hue angle arc tan b*/a*). When the desired silver endpoint has been reached, the mixture is stirred for a further 15 minutes.The pigment comprises 20% of precipitated SiO₂, based on the glassflakes.

The product is filtered off, washed, dried at 150° C. and calcinedat >700° C. The finished pigment is incorporated into a commerciallyavailable nitro-cellulose lacquer, and paint cards are prepared. Thepaint cards exhibit a very pure silver-white with high gloss. TABLE 4Glass compositions in % Constituent Glass C Glass D SiO₂ 65.7 64.8 Al₂O₃4.0 4.9 CaO 5.9 5.6 MgO 1.9 1.7 B₂O₃ 5.4 4.2 Na₂O + K₂O 12.7 14.7 ZnO4.3 3.9 FeO/Fe₂O₃ 0.1 0.2

Example 13

A silver-white pigment is prepared by the process described in Example12. Instead of glass flakes of composition C from Table 4, glass flakesof composition D having the same thickness and size distribution (20-200μm) are used. The titanium dioxide coating is carried out to the sameend point as in Example 12. The pigments obtained cannot bedistinguished visually from those from Example 12.

Examples 14-16

Silver-white pigments having the following proportions by weight ofSiO₂, based on the glass flakes, are prepared by the procedure indicatedin Example 12:

Example 14: 2% of SiO₂ by metered addition of 11.5 g of water-glasssolution dissolved in 11.5 g of water

Example 15: 5% of SiO₂ by metered addition of 28 g of water-glasssolution dissolved in 28 g of water

Example 16: 10% of SiO₂ by metered addition of 56 g of water-glasssolution dissolved in 56 g of water

The titanium dioxide coatings are carried out to the same hue as inExamples 12 and 13.

Examples 17 and 18 Comparative Examples without a First SiO₂ Layer

150 g of glass flakes of composition C from Table 4 having an averagelayer thickness of 900 nm are heated to 75° C. with stirring in 1.9 l ofdeionised water. The pH of the suspension is adjusted to pH 1.8 usinghydrochloric acid. Tin tetrachloride solution in hydrochloric acid (4.5g of SnCl₄*5 H₂O dissolved in 22.5 ml of 25% hydrochloric acid and 128ml of deionised water) is subsequently added dropwise, during which thepH is kept constant by simultaneous dropwise addition of 32% sodiumhydroxide solution. When the addition is complete, the mixture isstirred for a further 15 minutes. This is followed by metered additionof 30% titanium tetrachloride solution, during which the pH is keptconstant by simultaneous dropwise addition of 32% sodium hydroxidesolution. When the desired silver end point has been reached, themixture is stirred for a further 15 minutes.

The product is filtered off, washed and dried at 150° C. A sample of thepigment is calcined at 600° C. (Example 17), and another is calcined at700° C. (Example 18), in each case for 60 minutes.

The finished pigments are incorporated into a commercially availablenitro-cellulose lacquer, and paint cards are prepared using the lacquer.With the pigment calcined at 600° C., the paint cards exhibit a puresilver-white with good gloss, while in the case of the pigment calcinedat 700° C., the gloss is significantly reduced.

Example 19 Comparative Example

150 g of glass flakes of composition C from Table 4 having an averagelayer thickness of 900 nm are heated to 75° C. with stirring in 1.9 1 ofdeionised water. The pH is adjusted to 5.5. 180 ml of aluminium chloridesolution in hydrochloric acid (18 g of aluminium chloride hexahydrate)are added dropwise at 75° C. with stirring, during which the pH is heldat 5 using sodium hydroxide solution. When the addition is complete, themixture is stirred at 75° C. for a further 2 hours. The coated glassflakes are filtered off, washed, dried at 150° C. and dewatered at 400°C. for 30 minutes. After cooling, the glass flakes coated with aluminiumoxide (about 5% of Al₂O₃) are processed further using titanium dioxideby the procedure indicated in Example 17 to give a silver-white pigment.

Compared with the pigment in accordance with the prior art from Example17, the pigment from Example 19 shows absolutely no improvement ingloss, and compared with the pigments having an SiO₂ layer, the pigmentexhibits significantly lower gloss.

Example 20 Testing of the Mechanical Stability

The testing of the mechanical stability is carried out analogously toExample 9.

The pigments from Examples 12-18 are subjected to an abrasion test ofthis type. The results are shown in Table 5 and show that only thepigments according to the invention having an SiO₂ layer have adequatemechanical stability for cosmetic applications. TABLE 5 Abrasionstability Abrasion Pigment Glass type SiO₂ layer stability Experiment 12(invention) C approx. 90 nm 1 Experiment 13 (invention) D approx. 90 nm1 Experiment 14 (invention) C approx. 9 nm 3 Experiment 15 (invention) Capprox. 22.5 nm 2 Experiment 16 (invention) C approx. 45 nm 1 Experiment17 (comparison) C 0 5 Experiment 18 (comparison) C 0 5

Example 21

125 g of glass flakes (glass D from Table 4) having an average layerthickness of 500 nm are heated to 75° C. with stirring in 1.75 1 ofdeionised water. The pH of the suspension is then adjusted to 8 using 5%hydrochloric acid. Sodium water-glass solution (67 g of sodiumwater-glass solution comprising 26.8% of SiO₂ dissolved in 67 g ofdeionised water) is subsequently added dropwise, during which the pH iskept constant at 7.5 by simultaneous metered addition of 5% hydrochloricacid. When the addition is complete, the mixture is stirred for afurther 15 minutes. The pH of the suspension is then adjusted to 2.8,the mixture is stirred for a further 15 minutes, and about 320 ml of 15%iron chloride solution in hydrochloric acid are added dropwise, duringwhich the pH is kept constant by simultaneous dropwise addition of 32%sodium hydroxide solution. The coloristic properties of the pigment aremeasured as in Example 10 during the coating. When the addition iscomplete, the mixture is stirred for a further 15 minutes. The pigmentcomprises 10% of precipitated SiO₂, based on the glass flakes.

The product is filtered off, washed, dried at 150° C. and calcinedat >700° C.

The finished pigment is incorporated into a commercially availablenitro-cellulose lacquer, and paint cards are prepared. The paint cardsexhibit a very pure iron oxide red with high gloss.

Example 22

125 g of glass flakes (glass D from Table 4, particle sizes 10-60 μm)having an average layer thickness of 500 nm are heated to 75° C. withstirring in 1.75 l of deionised water. The pH of the suspension is thenadjusted to 7.5 using 5% hydrochloric acid. Sodium water-glass solution(67 g of sodium water-glass solution comprising 26.8% of SiO₂ dissolvedin 67 g of deionised water) is subsequently added dropwise, during whichthe pH is kept constant at 7.5 by simultaneous metered addition of 5%hydrochloric acid. When the addition is complete, the mixture is stirredfor a further 15 minutes.

The pH of the suspension is then adjusted to 1.8, the mixture is stirredfor a further 15 minutes, and tin tetrachloride solution in hydrochloricacid (2.5 g of SnCl₄*5 H₂O dissolved in 12.5 ml of 25% hydrochloric acidand 70 ml of deionised water) is added dropwise, during which the pH iskept constant by simultaneous dropwise addition of 32% sodium hydroxidesolution. When the addition is complete, the mixture is stirred for afurther 15 minutes.

The pH of the suspension is subsequently held at 1.8, and aqueoustitanium tetrachloride solution (400 g of TiCl₄/litre of solution) ismetered in at a rate of 2 ml/min, during which the pH is held at 1.7-1.9by addition of sodium hydroxide solution. The coloristic properties ofthe pigment are measured as in Example 10 during the TiO₂ coating. Whenthe requisite hue angle has been reached, the pH is adjusted slowly topH 8 by addition of 32% NaOH, and sodium water-glass solution (9.8 g ofsodium water-glass solution comprising 26.8% of SiO₂ dissolved in 9.8 gof deionised water) is again added dropwise, during which the pH is keptconstant at 7.5 by simultaneous metered addition of 5% hydrochloricacid. When the addition is complete, the mixture is stirred for afurther 15 minutes. The volume of the sodium water-glass solution mustbe calculated accurately since it is not possible to monitor colourformation in coloristic terms during the coating.

The pH is then again adjusted to pH 1.8 using 5% hydrochloric acid, andaqueous titanium tetrachloride solution (400 g of TiCl₄/litre ofsolution) is metered in at a rate of 2 ml/min, during which the pH isheld at 1.7-1.9 by addition of sodium hydroxide solution. The end pointof the titration is determined from the hue angle. The pigment comprises10% of precipitated SiO₂, based on the glass flakes.

The product is filtered off, washed, dried at 150° C. and calcinedat >700° C.

The finished pigment is incorporated into a commercially availablenitro-cellulose lacquer, and paint cards are prepared. The paint cardsexhibit a very pure and bright interference colour with high gloss.

1. Interference pigments based on coated flake-form substrates,characterised in that they comprise (A) a layer of SiO₂ having a layerthickness of 5-350 nm, (B) a high-refractive-index coating having arefractive index n of >1.8 and/or (C) an interference system consistingof alternating high- and low-refractive-index layers and optionally (D)an outer protective layer.
 2. Interference pigments according to claim1, characterised in that the flake-form substrates are natural and/orsynthetic mica, talc, kaolin, flake-form iron or aluminium oxides, glassflakes, SiO₂ flakes, TiO₂ flakes, graphite flakes, syntheticsupport-free flakes, titanium nitride, titanium silicide, liquid crystalpolymers (LCPs), holographic pigments, BiOCl or flake-form mixed oxides,or mixtures thereof.
 3. Interference pigments according to claim 2,characterised in that the flake-form substrates are glass flakes, micaflakes or aluminium oxide flakes.
 4. Interference pigments according toclaim 1, characterised in that the thickness of layer (A) is 30-100 nm.5. Interference pigments according to claim 1, characterised in thatlayer (A) is doped with carbon black particles, metal particles and/orcoloured pigments.
 6. Interference pigments according to claim 1,characterised in that layer (B) consists of metal oxides. 7.Interference pigments according to claim 6, characterised in that themetal oxides are TiO₂, ZrO₂, SnO₂, ZnO, Ce₂O₃, Fe₂O₃, Fe₃O₄, Cr₂O₃, CoO,Co₃O₄, VO₂, V₂O₃, NiO, titanium suboxides, or mixtures thereof. 8.Interference pigments according to claim 6, characterised in that layer(B) is titanium dioxide.
 9. Interference pigments according to claim 1,characterised in that layer (C) consists of alternating high- andlow-refractive-index layers.
 10. Interference pigments according toclaim 9, characterised in that layer (C) has a TiO₂—SiO₂—TiO₂ layersequence.
 11. Interference pigments according to claim 1, characterisedin that they have an outer protective layer (D) in order to increase thelight, temperature and weather stability.
 12. Process for thepreparation of the interference pigments according to claim 1,characterised in that the coating of the substrates is carried out bywet-chemical methods by hydrolytic decomposition of metal salts inaqueous medium or by gas-phase coating in a fluidised-bed reactor. 13.Use of the interference pigments according to claim 1 in paints,coatings, automotive paints, powder coatings, printing inks, securityprinting inks, plastics, ceramic materials, glasses, paper, in tonersfor electrophotographic printing processes, in seed, in greenhousesheeting and tent awnings, as absorbers in the laser marking of paperand plastics, in cosmetic formulations, for the preparation of pigmentpastes with water, organic and/or aqueous solvents, and for thepreparation of pigment preparations and dry preparations.